I have a newer 3dr iris+ and recently had a flight where the Mission stated an altitude of 200meters. It flew most of the way at the correct altitude, but towards the end it started to get low, to around 50 meters. I was watching and I switched it into loiter mode and put the throttle high up and it had no problem gaining altitude.The battery voltage was fine as well, as it was a short mission.What could cause this? I was using the droidplanner2 android software....I can provide logs if needed....Thanks in advance for your help!
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I am using the stock 3dr batteries. They are 8C batteries. They are light for the 5100mah compared to others I found online.
I understand what you're saying about maxing out the thrust, but when I put it in loiter i was able to increase the altitude extremely fast, from 40-100m or so. Was it because it wasn't in motion horizontally when I raised the altitude? (It was stationary when I flipped to loiter).
Well I always fully charge the battery using a balance charger to 4.2v per cell. I wont fly unless its fully charged. But I will change the failsafe mah value to 1250mah.
Does the pixhawk track the mah used? My remote has telemetry built in and gives me data on mah used. That failsafe value you mentioned earlier, that is the pixhawk monitoring it? If I unplug the battery on the quadcopter, will it reset the mah used? Sometimes the altimeter reads -1m when it should read 0m so I do a quick power cycle...
It's not specific to the Pixhawk, it just requires a voltage/current sensor. The current failsafe makes an assumption that you are always starting with a fully charged battery. It is also effected by the accuracy of you current sensor. For example your BATT_CAPACITY is set to 5100 and if you set FS_BATT_MAH to 1250 then when the FC THINKS you have used 3850mAh it will trigger failsafe. There are two problems here, the accuracy of your voltage/current sensor and the REAL full charge capacity of your battery. If you start out with a battery that has less than the 5100mAh available that you have told the FC you have, then the failsafe will be late triggering. Second if your current sensor is reading LOW then it will be under reporting current and your FC will trigger failsafe late.
I suspect in this flight in question you hadn't yet triggered a failsafe, but the FC wasn't able to develop adequate thrust to maintain altitude. The output of the motors was almost maxed out during the phase of the flight where you were losing altitude. Based on this I think the sagging voltage is limiting your flight time overall. Since your max rpm is based on the voltage supplied to the motors, having a battery that maintains higher voltage under load is important. Are you using a 3DR supplied battery, or are you using another brand? Are they new or a few years old? Have you tried doing a check of internal resistance?
Manned aircraft should be above 500 feet. For safety reasons all RC craft including quads should stay below 400 AGL. Imagine what could happen if a small plane hit a mutlirotor or how one would feel being responsible!
OK so here's what happened.....plain and simple, you just flew too long. Below is a graph of your second Auto flight. The trace on top shows your main battery voltage, the trace on the bottom is your altitude in meters relative to your "home" altitude. Your voltage starts at around 10.92v when you start this auto mission and when you switched to loiter mode to arrest your rapid descent and increased the throttle your main battery voltage momentarily sagged to as low as 5.8v!!! Once you stabilized your descent the battery still only was putting out around 7.9v. It's amazing you didn't have a brown out! I'm sure you already knew this but about half way through this auto mission the aircraft went into failsafe due to low battery.
I think all you need to do is pay closer attention to your battery level before engaging an auto mission.
As to the commercial/recreational aspect of the 400' rule, it is universal. We are all flying in the NAS and are limited to 400'.
Nathaniel Caner > Nathaniel CanerDecember 27, 2014 at 7:07pm
Adam,
Some other things to note:
Your battery failsafe is enabled, which is good, but you didn't give a value for MAH. I would suggest that this was your main problem. Since it is set to 0 it effectively does nothing. I believe you used more current than your sensor was reading and if it had been configured for current/consumed failsafe, it would have triggered earlier and would have landed safely. Your battery is listed as having a capacity of 5100mAh, I would suggest setting FS_BATT_MAH to between 1250 and 1300 to start.
Also I don't think your current sensor is properly calibrated. You used 4538mAh according to MP, which I think is probably a bit low unless the battery wasn't fully charged to begin with (always start with a fully charged battery in good condition). Follow the instructions here to calibrate the current sensor. I'm assuming this is a 3DR PM, if not the procedure is similar for other devices. Check the Table of contacts for the Attopilot sensor to see how to calibrate other sensors.
Regards,
Nathaniel ~KD2DEY
Adam S > Nathaniel CanerDecember 27, 2014 at 6:59pm
Hi Nathaniel. I just realized I uploaded the wrong log. The log you viewed was an actual crash I had at a small field near me. I did make a rookie mistake and was using my transmitter mah used to determine when to land. But the problem was I turned the remote off/on again, resetting the counter. Almost no damage (luckily) but I learned a lot.
The correct log is uploaded I believe. I'm sorry, I flew several flights a day and am having trouble remembering the order. This flight uploaded used auto pilot until the last minute or two, when I put it in loiter to raise the altitude. It should've maintained 200m the entire flight according to the droidplanner2 program.
Sorry to upload the wrong file. Trying to learn how to analyze these myself.
Replies
I understand what you're saying about maxing out the thrust, but when I put it in loiter i was able to increase the altitude extremely fast, from 40-100m or so. Was it because it wasn't in motion horizontally when I raised the altitude? (It was stationary when I flipped to loiter).
Does the pixhawk track the mah used? My remote has telemetry built in and gives me data on mah used. That failsafe value you mentioned earlier, that is the pixhawk monitoring it? If I unplug the battery on the quadcopter, will it reset the mah used? Sometimes the altimeter reads -1m when it should read 0m so I do a quick power cycle...
Adam,
It's not specific to the Pixhawk, it just requires a voltage/current sensor. The current failsafe makes an assumption that you are always starting with a fully charged battery. It is also effected by the accuracy of you current sensor. For example your BATT_CAPACITY is set to 5100 and if you set FS_BATT_MAH to 1250 then when the FC THINKS you have used 3850mAh it will trigger failsafe. There are two problems here, the accuracy of your voltage/current sensor and the REAL full charge capacity of your battery. If you start out with a battery that has less than the 5100mAh available that you have told the FC you have, then the failsafe will be late triggering. Second if your current sensor is reading LOW then it will be under reporting current and your FC will trigger failsafe late.
I suspect in this flight in question you hadn't yet triggered a failsafe, but the FC wasn't able to develop adequate thrust to maintain altitude. The output of the motors was almost maxed out during the phase of the flight where you were losing altitude. Based on this I think the sagging voltage is limiting your flight time overall. Since your max rpm is based on the voltage supplied to the motors, having a battery that maintains higher voltage under load is important. Are you using a 3DR supplied battery, or are you using another brand? Are they new or a few years old? Have you tried doing a check of internal resistance?
Regards,
Nathaniel ~KD2DEY
Manned aircraft should be above 500 feet. For safety reasons all RC craft including quads should stay below 400 AGL. Imagine what could happen if a small plane hit a mutlirotor or how one would feel being responsible!
Hey Adam,
OK so here's what happened.....plain and simple, you just flew too long. Below is a graph of your second Auto flight. The trace on top shows your main battery voltage, the trace on the bottom is your altitude in meters relative to your "home" altitude. Your voltage starts at around 10.92v when you start this auto mission and when you switched to loiter mode to arrest your rapid descent and increased the throttle your main battery voltage momentarily sagged to as low as 5.8v!!! Once you stabilized your descent the battery still only was putting out around 7.9v. It's amazing you didn't have a brown out! I'm sure you already knew this but about half way through this auto mission the aircraft went into failsafe due to low battery.
I think all you need to do is pay closer attention to your battery level before engaging an auto mission.
As to the commercial/recreational aspect of the 400' rule, it is universal. We are all flying in the NAS and are limited to 400'.
Regards,
Nathaniel ~KD2DEY
Adam,
Some other things to note:
Your battery failsafe is enabled, which is good, but you didn't give a value for MAH. I would suggest that this was your main problem. Since it is set to 0 it effectively does nothing. I believe you used more current than your sensor was reading and if it had been configured for current/consumed failsafe, it would have triggered earlier and would have landed safely. Your battery is listed as having a capacity of 5100mAh, I would suggest setting FS_BATT_MAH to between 1250 and 1300 to start.
FS_BATT_ENABLE 1
FS_BATT_MAH 0
FS_BATT_VOLTAGE 10.5
Also I don't think your current sensor is properly calibrated. You used 4538mAh according to MP, which I think is probably a bit low unless the battery wasn't fully charged to begin with (always start with a fully charged battery in good condition). Follow the instructions here to calibrate the current sensor. I'm assuming this is a 3DR PM, if not the procedure is similar for other devices. Check the Table of contacts for the Attopilot sensor to see how to calibrate other sensors.
Regards,
Nathaniel ~KD2DEY
Hi Nathaniel. I just realized I uploaded the wrong log. The log you viewed was an actual crash I had at a small field near me. I did make a rookie mistake and was using my transmitter mah used to determine when to land. But the problem was I turned the remote off/on again, resetting the counter. Almost no damage (luckily) but I learned a lot.
The correct log is uploaded I believe. I'm sorry, I flew several flights a day and am having trouble remembering the order. This flight uploaded used auto pilot until the last minute or two, when I put it in loiter to raise the altitude. It should've maintained 200m the entire flight according to the droidplanner2 program.
Sorry to upload the wrong file. Trying to learn how to analyze these myself.
2014-12-25 12-13-51.tlog
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